This invention relates to mechanically operated electric switches, particularly of the pushbutton operator type, which effect a momentary closing and reopening of a normally open pair of switch contacts during a single operation of the switch. Switches of this type may be referred to as single stroke make and break pushbuttons. More specifically, this invention relates to switches of the aforementioned type which are further categorized as palm switches which have utilization in anti-tie down control circuits for electrically controlled manufacturing apparatus which require the human operator of the apparatus to operate two spaced apart palm switches simultaneously to cycle the apparatus. This invention further relates to an anti-tie down control circuit of the aforementioned type utilizing the switches of this invention.
Manufacturing apparatus such as punches, presses, forming brakes, riveters and the like, require a human operator to position a work piece within the apparatus and to then operate one or more switches which will cause the apparatus to cycle driving a tool member down upon the work piece. For safety reasons, to insure that the human operator's hands are clear of the area of the work piece and tool at the time of impact, control systems for the apparatus commonly employ two spaced apart hand operated switches in the control circuit, each which must be operated to close its respective contacts during the same time interval to effect cycling of the apparatus. In order to increase production, human operators often defeat this safety feature by securing one of the hand operated switches in the contact closed position. As a result, manufacturers of the apparatus and the control systems therefor have devised more complex systems which are not susceptible to defeating the aforementioned safety feature. Such systems are referred to as anti-tie down systems and include additional control elements therein such as timing relays or the like which add to the initial cost and subsequent maintenance of the system and to the overall labor burden of the parts being manufactured